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The DICE calibration project. Design, characterization, and first results
Abstract and Figures
We describe the design, operation, and first results of a photometric
calibration project, called DICE (Direct Illumination Calibration Experiment),
aiming at achieving precise instrumental calibration of optical telescopes. The
heart of DICE is an illumination device composed of 24 narrow-spectrum,
high-intensity, light-emitting diodes (LED) chosen to cover the
ultraviolet-to-near-infrared spectral range. It implements a point-like source
placed at a finite distance from the telescope entrance pupil, yielding a flat
field illumination that covers the entire field of view of the imager. The
purpose of this system is to perform a lightweight routine monitoring of the
imager passbands with a precision better than 5 per-mil on the relative
passband normalisations and about 3{\AA} on the filter cutoff positions. The
light source is calibrated on a spectrophotometric bench. As our fundamental
metrology standard, we use a photodiode calibrated at NIST. The radiant
intensity of each beam is mapped, and spectra are measured for each LED. All
measurements are conducted at temperatures ranging from 0{\deg}C to 25{\deg}C
in order to study the temperature dependence of the system. The photometric and
spectroscopic measurements are combined into a model that predicts the spectral
intensity of the source as a function of temperature. We find that the
calibration beams are stable at the $10^{-4}$ level -- after taking the slight
temperature dependence of the LED emission properties into account. We show
that the spectral intensity of the source can be characterised with a precision
of 3{\AA} in wavelength. In flux, we reach an accuracy of about 0.2-0.5%
depending on how we understand the off-diagonal terms of the error budget
affecting the calibration of the NIST photodiode. With a routine 60-mn
calibration program, the apparatus is able to constrain the passbands at the
targeted precision levels.
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... Our method requires the brightness of the star to be constant; thus, the photoelectric detector at the exit pupil of the collimator is used to correct the output energy variation during the experiment. The photoelectric detector has high monitoring sensitivity and stability, and the stability can be better than 0.1%, indicating that the energy correction error has negligible effects on the calibration accuracy [24]. ...
Preflight ground flat-field calibration is significant to the development phase of space astronomical telescopes. The uniformity of the flat-field illumination reference source seriously decreases with the increasing aperture and the telescope’s field of view, directly affecting the final calibration accuracy. To overcome this problem, a flat-field calibration method that can complete calibration without a traditional flat-field illumination reference source is proposed on the basis of the spatial time-sharing calibration principle. First, the characteristics of the flat field in the spatial domain taken by the space astronomical telescope are analyzed, and the flat field is divided into large-scale flat (L-flat) and pixel-to-pixel flat (P-flat). They are then obtained via different calibration experiments and finally combined with the data fusion process. L-flat is obtained through star field observations and the corresponding L-flat extraction algorithm, which can obtain the best estimation of L-flat based on numerous photometry samples, thereby effectively improving calibration accuracy. The simulation model of flat-field calibration used for accuracy analysis is established. In particular, the error sources or experimental parameters that affect the accuracy of L-flat calibration are discussed in detail. Results of the accuracy analysis show that the combined uncertainty of the proposed calibration method can reach 0.78%. Meanwhile, experiments on an optic system with a $\Phi {142}\;{\rm mm}$ Φ 142 m m aperture are performed to verify the calibration method. Results demonstrate that the RMS values of the residual map are 0.720%, 0.565%, and 0.558% at the large-, middle-, and small-scale, respectively. The combined calibration uncertainty is 0.88%, which is generally consistent with the results of the accuracy analysis.
... Apertures on the outputs of the integrating spheres are collimated by mirrors and re-imaged onto the focal plane of the Super-Nova Integral Field Spectrograph (SNIFS). Two of the collimated beams is monitored by a Cooled Large Area Photodiode, 18 which provides normalization. In this case, full pupil illumination is traded off against using a collimated beam re-imaging system to project large (1 • ) spots onto the focal plane. ...
With the increasingly large number of type Ia supernova being detected by current-generation survey telescopes, and even more expected with the upcoming Rubin Observatory Legacy Survey of Space and Time, the precision of cosmological measurements will become limited by systematic uncertainties in flux calibration rather than statistical noise. One major source of systematic error in determining SNe Ia color evolution (needed for distance estimation) is uncertainty in telescope transmission, both within and between surveys. We introduce here the Collimated Beam Projector (CBP), which is meant to measure a telescope transmission with collimated light. The collimated beam more closely mimics a stellar wavefront as compared to flat-field based instruments, allowing for more precise handling of systematic errors such as those from ghosting and filter angle-of-incidence dependence. As a proof of concept, we present CBP measurements of the StarDICE prototype telescope, achieving a standard (1 sigma) uncertainty of 3 % on average over the full wavelength range measured with a single beam illumination.
... The common method is to use a luminous intensity standard lamp (SL) and a photometer to measure the luminous intensity of the calibration light source according to the equidistance method. For example, the radiometric calibration spectral source (RCSS) [16] in the James Webb Telescope and the direct illumination calibration experiment (DICE) [17] in the Sloan Digital Sky Survey project trace the stability of the light source to the national standards. However, the equidistance method of measuring the stability of the light source has the limitation that it cannot monitor the luminous intensity of the light source in real-time and the long term. ...
Flux calibration is an important test item in laboratory calibration experiments of space gaze cameras, which is the basis for obtaining high-precision scientific application data. In the flux calibration of a space gaze camera, the multi-field calibration method is adopted. The instability of the calibration light source will introduce uncertainty during the calibration process. When the spatial camera adopts the gaze imaging mode, the stability of the light source indicates the change in the total energy received by the image plane during the gaze time, which is characterized by relative uncertainty. When the luminous intensity standard lamp runs for the long-term calibration of the stability of the calibration light source, real-time performance and accuracy cannot be guaranteed. Therefore, it is proposed to use a photodetector to measure the stability of the calibration light source for long-term and real-time accurate measurements. First, the stability of the photodetector is calibrated using the light emitting diode; then, the stability of the calibration light source is measured using the photodetector; finally, the stability uncertainty of the calibration light source and the measurement uncertainty of the method is evaluated. The results of the simulation analysis and experimental verification indicate that the gaze time is 5 min and the sampling frequency of the photodetector is 15 Hz; for example, when the flux calibration time is 8 h, the stability uncertainty of the calibration source is 0.42%, and the relative measurement uncertainty is 0.01%.
... Fortunately there are paths forward for each of these. For survey flux calibration, dedicated programs are needed, and there are currently multiple paths underway to improve the fundamental calibration of SN Ia samples and how they are tied to various other samples (e.g., Regnault et al. 2015;Stubbs & Brown 2015;Narayan et al. 2019). There is also ongoing work (G. ...
We present constraints on cosmological parameters from the Pantheon+ analysis of 1701 light curves of 1550 distinct Type Ia supernovae (SNe Ia) ranging in redshift from z = 0.001 to 2.26. This work features an increased sample size from the addition of multiple cross-calibrated photometric systems of SNe covering an increased redshift span, and improved treatments of systematic uncertainties in comparison to the original Pantheon analysis, which together result in a factor of 2 improvement in cosmological constraining power. For a flat ΛCDM model, we find Ω M = 0.334 ± 0.018 from SNe Ia alone. For a flat w 0 CDM model, we measure w 0 = −0.90 ± 0.14 from SNe Ia alone, H 0 = 73.5 ± 1.1 km s ⁻¹ Mpc ⁻¹ when including the Cepheid host distances and covariance (SH0ES), and w 0 = − 0.978 − 0.031 + 0.024 when combining the SN likelihood with Planck constraints from the cosmic microwave background (CMB) and baryon acoustic oscillations (BAO); both w 0 values are consistent with a cosmological constant. We also present the most precise measurements to date on the evolution of dark energy in a flat w 0 w a CDM universe, and measure w a = − 0.1 − 2.0 + 0.9 from Pantheon+ SNe Ia alone, H 0 = 73.3 ± 1.1 km s ⁻¹ Mpc ⁻¹ when including SH0ES Cepheid distances, and w a = − 0.65 − 0.32 + 0.28 when combining Pantheon+ SNe Ia with CMB and BAO data. Finally, we find that systematic uncertainties in the use of SNe Ia along the distance ladder comprise less than one-third of the total uncertainty in the measurement of H 0 and cannot explain the present “Hubble tension” between local measurements and early universe predictions from the cosmological model.
... calibrated photodiodes) instead of a stellar standard reference. This allows to improve the calibration accuracy from the 1-2% achievable with photometric standards to 0.2-0.5% [78]. ...
Supernovae (SNe) are luminous optical transients, which, despite being rare events in a single galaxy, nowadays are discovered at a rate of ten per day. They populate a growing zoo of different types linked to a variety of progenitors and explosion mechanisms. Through a biased selection of a century of researches, I will review how SNe have became a leading tool to probe the cosmic expansion. I will mainly focus on SNe of type Ia, originating from the thermonuclear explosion of white dwarfs, that were demonstrated to be excellent distance indicators after proper calibration and standardisation. Two decades ago, SNe Ia provided the surprising result that the cosmic expansion is accelerated by a misterious dark energy. Recently, with the decisive contribution of Cepheids variables as primary distance indicators, SN Ia allowed to measure the value of the Hubble-Lemaître constant, $$H_0$$ H 0 , with an error of only 1%. It turned out that the value of $$H_0$$ H 0 based on SNe Ia is in tension with the one measured through the fit of the CMB fluctuations. If confirmed, this finding requires a deep revision of the standard cosmological model.
... With larger datasets, modeling of many of the SN and host population related systematics will naturally improve. On the other hand, for flux calibration, dedicated programs are needed and thankfully there are multiple paths to improving the fundamental calibration of SN Ia samples and how they are tied to various other samples (e.g., Regnault et al. 2015;Narayan et al. 2019;Stubbs & Brown 2015). ...
We present constraints on cosmological parameters from the Pantheon+ analysis of 1701 light curves of 1550 distinct Type Ia supernovae (SNe Ia) ranging in redshift from $z=0.001$ to 2.26. This work features an increased sample size, increased redshift span, and improved treatment of systematic uncertainties in comparison to the original Pantheon analysis and results in a factor of two improvement in cosmological constraining power. For a Flat$\Lambda$CDM model, we find $\Omega_M=0.338\pm0.018$ from SNe Ia alone. For a Flat$w_0$CDM model, we measure $w_0=-0.89\pm0.13$ from SNe Ia alone, H$_0=72.86^{+0.94}_{-1.06}$ km s$^{-1}$ Mpc$^{-1}$ when including the Cepheid host distances and covariance (SH0ES), and $w_0=-0.978^{+0.024}_{-0.031}$ when combining the SN likelihood with constraints from the cosmic microwave background (CMB) and baryon acoustic oscillations (BAO); both $w_0$ values are consistent with a cosmological constant. We also present the most precise measurements to date on the evolution of dark energy in a Flat$w_0w_a$CDM universe, and measure $w_a=-0.4^{+1.0}_{-1.8}$ from Pantheon+ alone, H$_0=73.40^{+0.99}_{-1.22}$ km s$^{-1}$ Mpc$^{-1}$ when including SH0ES, and $w_a=-0.65^{+0.28}_{-0.32}$ when combining Pantheon+ with CMB and BAO data. Finally, we find that systematic uncertainties in the use of SNe Ia along the distance ladder comprise less than one third of the total uncertainty in the measurement of H$_0$ and cannot explain the present "Hubble tension" between local measurements and early-Universe predictions from the cosmological model.
... A supplemental approach that isolates the instrument throughput is to use well-characterized sensors as the metrology standard for relative flux determination. [6][7][8][9][10] In this approach, a well-calibrated photodetector, known to better than a part per thousand, 11 is used to map out the instrument's relative sensitivity versus wavelength. Conventional photon-detectors [photodiodes (PDs), CCDs, etc.] have collection areas no larger than a few square centimeters. ...
Type Ia supernovae are the most direct cosmological probe to study dark energy in the recent Universe, for which the photometric calibration of astronomical instruments remains one major source of systematic uncertainties. To address this, recent advancements introduce Collimated Beam Projectors (CBP), aiming to enhance calibration by precisely measuring a telescope’s throughput as a function of wavelength. This work describes the performance of a prototype portable CBP. The experimental setup consists of a broadband Xenon light source replacing a more customary but much more demanding high-power laser source, coupled with a monochromator emitting light inside an integrating sphere monitored with a photodiode and a spectrograph. Light is injected at the focus of the CBP telescope projecting a collimated beam onto a solar cell whose quantum efficiency has been obtained by comparison with a NIST-calibrated photodiode. The throughput and signal-to-noise ratio achieved by comparing the photocurrent signal in the CBP photodiode to the one in the solar cell are computed. We prove that the prototype, in its current state of development, is capable of achieving 1.2 per cent and 2.3 per cent precision on the integrated g and r bands of the ZTF photometric filter system respectively, in a reasonable amount of integration time. Central wavelength determination accuracy is kept below ∼ 0.91 nm and ∼ 0.58 nm for g and r bands. The expected photometric uncertainty caused by filter throughput measurement is approximately 5 mmag on the zero-point magnitude. Several straightforward improvement paths are discussed to upgrade the current setup.
As the precision frontier of astrophysics advances toward the one millimagnitude level, flux calibration of photometric instrumentation remains an ongoing challenge. We present the results of a lab-bench assessment of the viability of monocrystalline silicon solar cells to serve as large-aperture (up to 125[Formula: see text]mm diameter), high-precision photodetectors. We measure the electrical properties, spatial response uniformity, quantum efficiency (QE), and frequency response of third-generation C60 solar cells, manufactured by Sunpower. Our new results, combined with our previous study of these cells’ linearity, dark current, and noise characteristics, suggest that these devices hold considerable promise, with QE and linearity that rival those of traditional, small-aperture photodiodes. We argue that any photocalibration project that relies on precise knowledge of the intensity of a large-diameter optical beam should consider using solar cells as calibrating photodetectors.
While conventional Type Ia supernova (SN Ia) cosmology analyses rely primarily on rest-frame optical light curves to determine distances, SNe Ia are excellent standard candles in near-infrared (NIR) light, which is significantly less sensitive to dust extinction. A SN Ia spectral energy distribution (SED) model capable of fitting rest-frame NIR observations is necessary to fully leverage current and future SN Ia datasets from ground- and space-based telescopes including HST, LSST, JWST, and RST. We construct a hierarchical Bayesian model for SN Ia SEDs, continuous over time and wavelength, from the optical to NIR (B through H, or 0.35 − 1.8 μm). We model the SED as a combination of physically-distinct host galaxy dust and intrinsic spectral components. The distribution of intrinsic SEDs over time and wavelength is modelled with probabilistic functional principal components and the covariance of residual functions. We train the model on a nearby sample of 79 SNe Ia with joint optical and NIR light curves by sampling the global posterior distribution over dust and intrinsic latent variables, SED components and population hyperparameters. Photometric distances of SNe Ia with NIR data near maximum obtain a total RMS error of 0.10 mag with our BayeSN model, compared to 0.13-0.14 mag with SALT2 and SNooPy for the same sample. Jointly fitting the optical and NIR data of the full sample up to moderate reddening (host E(B − V) < 0.4) for a global host dust law, we find RV = 2.9 ± 0.2, consistent with the Milky Way average.
We present cosmological constraints from a joint analysis of type Ia
supernova (SN Ia) observations obtained by the SDSS-II and SNLS collaborations.
The data set includes several low-redshift samples (z<0.1), all 3 seasons from
the SDSS-II (0.05 < z < 0.4), and 3 years from SNLS (0.2 <z < 1) and totals
\ntotc spectroscopically confirmed type Ia supernovae with high quality light
curves. We have followed the methods and assumptions of the SNLS 3-year data
analysis except for the following important improvements: 1) the addition of
the full SDSS-II spectroscopically-confirmed SN Ia sample in both the training
of the SALT2 light curve model and in the Hubble diagram analysis (\nsdssc
SNe), 2) inter-calibration of the SNLS and SDSS surveys and reduced systematic
uncertainties in the photometric calibration, performed blindly with respect to
the cosmology analysis, and 3) a thorough investigation of systematic errors
associated with the SALT2 modeling of SN Ia light-curves. We produce
recalibrated SN Ia light-curves and associated distances for the SDSS-II and
SNLS samples. The large SDSS-II sample provides an effective, independent,
low-z anchor for the Hubble diagram and reduces the systematic error from
calibration systematics in the low-z SN sample. For a flat LCDM cosmology we
find Omega_m=0.295+-0.034 (stat+sys), a value consistent with the most recent
CMB measurement from the Planck and WMAP experiments. Our result is 1.8sigma
(stat+sys) different than the previously published result of SNLS 3-year data.
The change is due primarily to improvements in the SNLS photometric
calibration. When combined with CMB constraints, we measure a constant
dark-energy equation of state parameter w=-1.018+-0.057 (stat+sys) for a flat
universe. Adding BAO distance measurements gives similar constraints:
w=-1.027+-0.055.
We present a combined photometric calibration of the SNLS and the SDSS
supernova survey, which results from a joint effort of the SDSS and the SNLS
collaborations. We deliver fluxes calibrated to the HST spectrophotometric star
network for large sets of tertiary stars that cover the science fields of both
surveys in all photometric bands. We also cross-calibrate directly the two
surveys and demonstrate their consistency. For each survey the flat-fielding is
revised based on the analysis of dithered star observations. The calibration
transfer from the HST spectrophotometric standard stars to the multi-epoch
tertiary standard star catalogs in the science fields follows three different
paths: observations of primary standard stars with the SDSS PT telescope;
observations of Landolt secondary standard stars with SNLS MegaCam instrument
at CFHT; and direct observation of faint HST standard stars with MegaCam. In
addition, the tertiary stars for the two surveys are cross-calibrated using
dedicated MegaCam observations of stripe 82. This overlap enables the
comparison of these three calibration paths and justifies using their
combination to improve the calibration accuracy. Flat-field corrections have
improved the uniformity of each survey as demonstrated by the comparison of
photometry in overlapping fields: the rms of the difference between the two
surveys is 3 mmag in gri, 4 mmag in z and 8 mmag in u. We also find a
remarkable agreement (better than 1%) between the SDSS and the SNLS calibration
in griz. The cross-calibration and the introduction of direct calibration
observations bring redundancy and strengthen the confidence in the resulting
calibration. We conclude that the surveys are calibrated to the HST with a
precision of about 0.4% in griz. This precision is comparable to the external
uncertainty affecting the color of the HST primary standard stars.
We report on work to increase the number of well-measured Type Ia supernovae (SNe Ia) at high redshifts. Light curves, including high signal-to-noise Hubble Space Telescope data, and spectra of six SNe Ia that were discovered during 2001, are presented. Additionally, for the two SNe with z > 1, we present ground-based J-band photometry from Gemini and the Very Large Telescope. These are among the most distant SNe Ia for which ground-based near-IR observations have been obtained. We add these six SNe Ia together with other data sets that have recently become available in the literature to the Union compilation. We have made a number of refinements to the Union analysis chain, the most important ones being the refitting of all light curves with the SALT2 fitter and an improved handling of systematic errors. We call this new compilation, consisting of 557 SNe, the Union2 compilation. The flat concordance ΛCDM model remains an excellent fit to the Union2 data with the best-fit constant equation-of-state parameter w = –0.997+0.050 –0.054(stat)+0.077 –0.082(stat + sys together) for a flat universe, or w = –1.038+0.056 –0.059(stat)+0.093 –0.097(stat + sys together) with curvature. We also present improved constraints on w(z). While no significant change in w with redshift is detected, there is still considerable room for evolution in w. The strength of the constraints depends strongly on redshift. In particular, at z 1, the existence and nature of dark energy are only weakly constrained by the data.
MegaCam is an imaging camera with a 1 square degree field of view for the new prime focus of the 3.6 meter Canada-France-Hawaii Telescope. This instrument will mainly be used for large deep surveys ranging from a few to several thousands of square degrees in sky coverage and from 24 to 28.5 in magnitude. The camera is built around a CCD mosaic approximately 3 0 cm square, made of 40 large thinned CCD devices for a total of 20 K x 18 K pixels. It uses a custom CCD controller, a closed cycle cryocooler based on a pulse tube, a 1 m diameter half-disk as a shutter, a Juke-box for the selection of the filters, and programmable logic controllers and fieldbus network to control the different subsystems. The instrument was delivered to the observatory on June 10, 2002 and first light is scheduled in early October 2002.
The measurement of precise absolute fluxes for stellar sources has been
pursued with increased vigor since the discovery of the dark energy and the
realization that its detailed understanding requires accurate spectral energy
distributions (SEDs) of redshifted Ia supernovae in the rest frame. The flux
distributions of spectrophotometric standard stars were initially derived from
the comparison of stars to laboratory sources of known flux but are now mostly
based on calculated model atmospheres. For example, pure hydrogen white dwarf
(WD) models provide the basis for the HST CALSPEC archive of flux standards.
The basic equations for quantitative spectrophotometry and photometry are
explained in detail. Several historical lab based flux calibrations are
reviewed; and the SEDs of stars in the major on-line astronomical databases are
compared to the CALSPEC reference standard spectrophotometry. There is good
evidence that relative fluxes from the visible to the near-IR wavelength of
~2.5 micron are currently accurate to 1% for the primary reference standards;
and new comparisons with lab flux standards show promise for improving that
precision.
H-rich, DA-type white dwarfs are particularly suited as primary standard
stars for flux calibration. State-of-the-art NLTE models consider opacities of
species up to trans-iron elements and provide reliable synthetic
stellar-atmosphere spectra to compare with observation.
We establish a database of theoretical spectra of stellar flux standards that
are easily accessible via a web interface.
In the framework of the Virtual Observatory, the German Astrophysical Virtual
Observatory developed the registered service TheoSSA. It provides easy access
to stellar spectral energy distributions (SEDs) and is intended to ingest SEDs
calculated by any model-atmosphere code. In case of the DA white dwarf G
191-B2B, we demonstrate that the model reproduces not only its overall
continuum shape but also the numerous metal lines exhibited in its ultraviolet
spectrum.
TheoSSA is in operation and contains presently a variety of SEDs for DA white
dwarfs. It will be extended in the near future and can host SEDs of all primary
and secondary flux standards. The spectral analysis of G 191-B2B has shown that
our hydrostatic models reproduce the observations best at an effective
temperature of 60000 +/- 2000K and a surface gravity of log g = 7.60 +/- 0.05.
We newly identified Fe VI, Ni VI, and Zn IV lines. For the first time, we
determined the photospheric zinc abundance with a logarithmic mass fraction of
-4.89 (7.5 times solar). The abundances of He (upper limit), C, N, O, Al, Si,
O, P, S, Fe, Ni, Ge, and Sn were precisely determined. Upper abundance limits
of 10% solar were derived for Ti, Cr, Mn, and Co.
The TheoSSA database of theoretical SEDs of stellar flux standards guarantees
that the flux calibration of all astronomical data and cross-calibration
between different instruments can be based on the same models and SEDs
calculated with different model-atmosphere codes and are easy to compare.
This is the thoroughly revised and updated second edition of the hugely successful The Art of Electronics. Widely accepted as the single authoritative text and reference on electronic circuit design, both analog and digital, the original edition sold over 125,000 copies worldwide and was translated into eight languages. The book revolutionized the teaching of electronics by emphasizing the methods actually used by citcuit designers - a combination of some basic laws, rules to thumb, and a large nonmathematical treatment that encourages circuit values and performance. The new Art of Electronics retains the feeling of informality and easy access that helped make the first edition so successful and popular. It is an ideal first textbook on electronics for scientists and engineers and an indispensable reference for anyone, professional or amateur, who works with electronic circuits. The best self-teaching book and reference book in electronics Simply indispensable, packed with essential information for all scientists and engineers who build electronic circuits Totally rewritten chapters on microcomputers and microprocessors The first edition of this book has sold over 100,000 copies in seven years, it has a market in virtually all research centres where electronics is important
For both the Lick and the Palomar calibrations of the spectral-energy
distribution of Vega, the atmospheric extinction was treated
incorrectly. A model is presented for extinction in the earth's
atmosphere and this model is used to calculate corrections to the Lick
and Palomar calibrations. A method is described that can be used to
fabricate mean extinction coefficients for any mountain observatory.
Selected portions of the corrected Lick and corrected Palomar
calibrations are combined with the new Mount Hopkins calibration to
generate an absolute spectral-energy distribution of Vega over the
wavelength range 3300-10,800 A. Until better measurements become
available, the use of this calibration is recommended for all practical
applications.
The monochromatic illumination system is constructed to carry out in situ measurements of the response function of the mosaicked CCD imager used in the Sloan Digital Sky Survey (SDSS). The system is outlined and the results of the measurements, mostly during the first six years of the SDSS, are described. We present the reference response functions for the five color passbands derived from these measurements, and discuss column-to-column variations and variations in time, and also their effects on photometry. We also discuss the effect arising from various, slightly different response functions of the associated detector systems that were used to give SDSS photometry. We show that the calibration procedures of SDSS remove these variations reasonably well with the resulting final errors from variant response functions being unlikely to be larger than 0.01 mag for g, r, i, and z bands over the entire duration of the survey. The considerable aging effect is uncovered in the u band, the response function showing a 30% decrease in the throughput in the short wavelength side during the survey years, which potentially causes a systematic error in photometry. The aging effect is consistent with variation of the instrumental sensitivity in the u band, which is calibrated out. The expected color variation is consistent with measured color variation in the catalog of repeated photometry. The color variation is Δ(u – g) ~ 0.01 for most stars, and at most Δ(u – g) ~ 0.02 mag for those with extreme colors. We verified in the final catalog that no systematic variations in excess of 0.01 mag are detected in the photometry which can be ascribed to aging and/or seasonal effects except for the secular u – g color variation for stars with extreme colors.
We describe the concept of modularity and versatility in the construction of a new cryogenic radiometer developed at the National Institute of Standards and Technology. We address the benefits of the modular design in the construction and development and discuss some of the device characterizations and results of a cryogenic radiometer intercomparison.